Liquid crystal electric field sensing measurement and display device

ABSTRACT

A flat panel, electric field controlled device is provided for the measurement and display of electrical parameters such as voltage, the voltage sensing effect being provided by a nematic liquid crystal medium having high positive dielectric anisotropy and placed in a thin flat-sided optically transparent cell. Optical transmission of the nematic liquid crystal medium is controlled by voltages applied to interdigital arrays of parallel electrode elements affixed on the inner surface of only one of the transparent parallel cell walls. Continuous relative changes in the respective potentials applied to the electrode arrays provide continuous analog movement of the borders between birefringent and non-birefringent areas formed in the liquid crystal medium.

7 United Statt j i;c .zo [11] 3,834,794

I Soref [451 Sept. 10, 1974 LIQUID CRYSTAL ELECTRIC FIELD PrimaryExaminer-Ronald L. Wibert SENSING MEASUREMENT AND DISPLAY AssistantExaminer-Paul K. Godwin DEVlCE Attorney, Agent, or Firm-R. J.Steinmeyer; J. M.

Thomson [75] Inventor: Richard A. Soref, Chestnut Hill,

Mass. [73] Assignee: Beckman Instruments, Inc., [57] ,ABSTRACT FullertonCam A flat panel, electric field controlled device is provided for themeasurement and display of electrical [22] Flled: June 1973 parameterssuch as voltage, the voltage sensing effect [21] APPL 374,460 beingprovided by a nematic liquid crystal medium having high positivedielectric anisotropy and placed in a thin flat-sided opticallytransparent cell. Optical [52] US. Cl. 350/160 LC transmission f thenematic quid crystal medium is ll!- CI. controlled voltages to intrdlgit l ar f [58] Field of Search 350/160 LC, 160 R parallel electrodeelements ffi d on the inner Sup face of only one of the transparentparallel cell walls.

7' I '7 I 7 Continuous relative chan es in the res ective tenl lReferences Cited g P P tials applied to the electrode arrays providecontinu- UNITED STATES PATENTS ous analog movement of the bordersbetween birefrin- 3,674,342 7/1972 Castellano et al. 350/160 LC gem andHQH-birefringem areas formed in the liquid 3,727,527 8/1973 Borowski etal 350/ I60 LC crystal medium.

10 Claims, 6 DrawingFigures POLA EIZER a P we PATENTEBSEPI 01914 SHEEI 2OF 2 FIG.4.

F'IG.3.

FIG.6.

LIQUID CRYSTAL ELECTRIC FIELD SENSING MEASUREMENT AND DISPLAY DEVICEBACKGROUND OF THE INVENTION 1. Field of the Invention The inventionrelates to electrically controllable panel display devices employingpositive dielectric anisotropy liquid crystalline materials as electricfield active media and more particularly relates to such display devicesin which the size, shape, or location of twodimensional display patternsmay be changed continuously in analog fashion.

2. Description of the Prior Art Nematic liquid crystal materials havebeen found in the past to offer utility in electric current controlledturbulence effect displays of the flat panel type. Such displays havegenerally been realized in types which vary the size, shape, or locationof the display pattern in a discontinuous or digital fashion, though theR. A. Soref U.S. Pat. No. 3,675,988 for Liquid Crystal Electro-OpticalMeasurement and Display Devices," issued July I 1, 1972 and assigned tothe Sperry Rand Corporation, illustrates a continuously variable analogdisplay device which may be used as a turbulence display and over whichthe present invention is an improvement.

While prior art turbulence displays make advantageous use of some of theproperties of liquid crystal compositions, they tend to be short lived,since the primary phenomenon producing the display involves turbulenceeffects caused directly by electrical current flow through the liquidcrystal medium; i.e., the materials are electric current sensitivematerials and are not directly voltage sensors. Such current flowrequires the use of excessive power and tends to cause the liquidcrystal materials to deteriorate, seriously reducing the life span ofthe display.

While the device of the Soref patent may be used with liquid crystalmaterials of various types, including those demonstrating electric fieldsensitive birefringence or rotary electro-optical effects, display cellsaccommodating very thin layers of nematic materials are preferred forthe latter kinds of operations. Furthermore, the prior art displays useelectrode systems on surfaces of both principal wall elements of thecell, which electrode systems require careful alignment duringassemblyand are therefore expensive to produce. Such prior art devices,having conducting electrodes on each side of the nematic layer, are alsosubject to accidental short circuiting between electrode systems,especially when attempts to make thin cells are made.

SUMMARY OF THE INVENTION The invention is an electric-field controlled,electrooptical analog measurement or display device of the panel typewhich includes a very thin layer of positive dielectric anisotropynematic liquid crystalline material directly responsive to electricfields imposed within the nematic material itself and thereforeovercoming defects present in the prior art. The invention may employthe basic concepts of the R. A. Soref U.S. Pat. application Ser. No.264,679 for a Liquid Crystal Display," filed June 20, 1972 and assignedto the Sperry Rand Corporation. As in the latter Soref application, thenematic material is placed within a thin cell having transparent frontand rear cell wall elements with precisely parallel flat sides. Theelectric control field threading the nematic layer is provided by anarray of electrodes placed only on one inner surface of one of thecell-defining wall elements. Birefringence or rotary electro-optiealeffects of the nematic liquid crystal are controlled by selectedvoltages applied to the interleaved or interdigital electrode sets whichconstitute a pair of coplanar cooperating electrode systems, the pairbeing formed on the inner surface of the one cell side.

One set of digital electrode elements may be operated at a selectedpotential from a first source, while individuals of the second set areoperated at progressively varying potentials through the use of a highimpedance distributor conductor across which a second potential sourceis connected. If the first voltage is held constant while the second isvaried, a dark, narrow but fixed-width image simulating, for example, avoltmeter needle may be moved across the display. Other display effectsanalogous to the analog displays of the aforementioned Soref U.S. Pat.No. 3,675,988 may readily be achieved.

Thus, an analog display is realized employing voltage sensitive liquidcrystal materials and birefringence or rotary electro-optical effects ina thin display cell. Alignment of the electrode sets may be accomplishedautomatically in one easy photographic step, manufacture and assembly ofthe device being significantly simplified. Because electric controlfield effects are directly employed, operating power is reduced and thelife expectancy of the display cell is increased. Unifonnity ofconstruction and long useful life are assured by forming mesas on one orthe other of the cell walls or plates, which mesas precisely define thethickness of the nematic layer. The mesa construction permanentlydefines the width of the active nematic layer, confining it uniformly toa selected width as small as 0.5 microns. Wide angle viewing isattained, as well as relative freedom from parallax effects and fromstray specular reflections.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation cross sectionview of one form of the invention.

FIG. 2 is a cross section of the FIG. 1 structure taken along the line2-2.

FIGS. 3 and 4 are graphs useful in explaining the operation of theinvention.

FIG. 5 is an enlarged cross section view of a portion of FIG. 1 forillustrating electric field configurations employed in the invention.

FIG. 6 is similar to FIG. 2 showing in cross section a plan view of analternative form of FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The novel electrical display ormeter is illustrated in FIGS. 1 and 2 in the form of an electric fieldcontrolled flat panel display device utilizing a pair of parallel-sidedflat glass or optically transparent dielectric plates 10 and 11, plate11 being specially shaped in order to accommodate a very thin layer ofelectric field sensitive liquid crystal material 12 particularly withinan interior region of the device, as will be explained. Plate 11 may bespaced from plate 10 by a plurality of mesa spacers such as spacers 14,l5, l6, and 17 formed integrally with the inner surface of plate 11.Mesa spacers 14, 15, 16, and 17 are placed conveniently on the innersurface of plate 11 so as not to interfere with the location of theactive interdigital electrode system 20 coated on only one or the otherof the interior surfaces of the respective plates or 11.

It will be understood that the proportions used in FIG. 1 areappropriately distorted so as to make the figure readily understandable.For example. the electrode system 20 yet to be described must beextremely thin, for example about 400 Angstrom units thick, as it isoptically transparent. The thickness of the region between plates 10 and11 enclosing liquid crystal layer 12 is so small as to provide importantresults, as will be further described, not available in the prior artturbulence type of liquid crystal display.

Electrode system 20 comprises parallel-disposed conductive and opticallytransparent electrode elements, such as electrode element 61, coupled toan elongate distributor conductor 25 having an exterior terminal 26.Electrode system 20 also includes parallelarranged conductive andoptically transparent electrode elements such as elements 60 and 62coupled to an elongate distributor conductor 31 having an externalelectrical terminal 27. The electrodes 60 and 61,

for example, may be spaced apart about 12 microns (24 micronscenter-to-center) and be 10 to microns wide. The respective electrodesof the arrays including electrodes 60 and 61 are arranged in parallelinterdigital fashion, as seen particularly in FIG. 2. By virtue of theirrelatively low resistance, the terminal 26, the elongate distributorconductor 25, and the array of electrode elements such as electrodeelement 61 are substantially equipotential surfaces and all comesubstantially instantaneously to the potential applied at terminal 26.

In the cooperating digital electrode array including electrode elementssuch as elements 60 and 62, these electrode elements are also lowresistance transparent electrodes. The character of the elongatedistributor conductor 31 is, however, distinct from that of elongatedistributor conductor 25 in that it demonstrates relatively highimpedance or resistivity characteristics. Section 54 of distributor 31may have the same conductivity as elongate distributor conductor 25, butit is provided with other series connected sections 55, 56, 57, 58, and59 which may be of substantially equal lengths, for example, which haveprogressively lower conductivities. Such different resistance sectionsmay be readily achieved in well known ways by the control of thethickness of the indium or tin oxide layer forming elongate distributorconductor 31, by control of its width, or by other well knowntechniques, such controls being exercised as the arrays are formed. Thedifferent resistances may also'be achieved in a conventional way byetching or otherwise progressively removing more and more of the tin orindium oxide layer during manufacture.

Accordingly, when a significant potential difference is applied betweenthe effective ends of elongate distributor conductor 31, the potentialsat each of the junctions between the adjacent sections 54, 55, 56, 57,58, and 59 progressively increase or decrease nonlinearly (FIG. 2), asdesired. Thus, the transparent lowresistivity electrode elements 60, 62,64, 65, 66, and 67, if coupled respectively to the junctions betweensections 54, 55, 56, 57, and 59 may each find themselves atprogressively different potential levels. An external end of elongatedistributor conductor 31 is supplied with a terminal 27. The oppositeend of elongate distributor conductor 31 is connected by preferably lowresistance conductors 32 and 33 to a terminal 28 conveniently locatednear terminal 27 so that terminals 20, 27, and 28 may be located all atone end of the display. A linear increase in potential can be obtainedwith non-tapered sections between digits, as illustrated in FIG. 6.

Dielectric plates 10 and 11 may be constructed from any suitable glassor generally from a transparent insulating material compatible with theoptical and hermetic sealing requirements of the display cell system.For example, the material may be selected to have an optical index ofrefraction similar to that of the electric field sensitive or nematicmaterial 12 so as to avoid undesired reflections at optical interfaces.So that the active material may be preserved in its pure form andprotected from contaminants and also remain uniform in thickness, aquadrilateral dielectric wall 37 is fonned as a continuous enclosurewall at the four edges of plates 10 and 11. Construction of the devicemay be generally according to techniques described by R. A. Soref and R.A. Carey in the U.S. patent application Ser. No. 331,436 for LiquidCrystal Display Apparatus," filed Feb. 12, 1973 and assigned to theSperry Rand Corporation and by R. A. Soref in the U.S. patentapplication Ser. No. 33l,437 for Liquid Crystal Reflective DisplayApparatus, filed Feb. 12, 1973, and assigned to the Sperry RandCorporation. Such construction permits the thickness of the liquidcrystal medium to lie between 0.5 to 2.5 microns or, preferably, between1.4 and 1.9 microns.

Referring especially to FIG. 2, it will be seen that particular arraysof electrodes such as that employing array electrode element 61 and thatemploying elements 60 and 62 are shown; it will be understood that thefigures are drawn in such proportions particularly for illustrating thebasic principles of the invention with clarity. In actual practice, anarray of many thin and closely spaced electrode elements such aselectrode element 61 will be used, with closely spaced interdigitallylocated electrode elements such as electrode elements 60 and 62.Electrode elements 60 and 62 may be instantaneously negative. forinstance, while electrode element 61 may be instantaneously positive. Insuch a case, instantaneous electric fields are set up between theseveral alternate electrode elements. As in FIG. 5, an electric field ofone sense may be found in the region between the oppositely poledelectrode elements 60 and 61, while an electric field of a reversedsense is found between electrode elements 61 and 62. The electric fieldslie primarily parallel to plates 10 and 11. although the fields alsofringe somewhat in other directrons.

Accordingly. the one set of interdigital electrode elements such aselement 61 attached to elongate distributor conductor 25 all reach thepotential applied at terminal 26 when a voltage source 34, which may bevariable, is connected between terminals 26 and 27. When a secondvoltage source 35, which may be variable, is connected across theelongate resistive distributor conductor 31, electrode elements 60, 62,64, 65, 66, and 67 arrive at successively different potentials withrespect to all of the elements of the array including electrode element61. Thus, for electrode elements 60, 62, 64, 65, 66, 67, potentialdifferences are provided between those same electrode elements by thesuccessive high impedance paths 54 through 59. Thus, the potential Vbetween adjacent electrode elements (of different arrays) varies as afunction of the distance x along the elongate distributor conductors and31.

It will be seen that manipulation of the voltages V, and V from voltagesources 34 and will determine which adjacent set of electrode elements,such as electrode elements 60, 61, will cause a display to occur. In onemode of operation, for example, a variable reference voltage V, issupplied across terminals 27 and 28 and thus across the sections 55, 56.57, S8, and 59 of resistive distributor conductor 31. At the same time,an unknown voltage V, may be supplied by a source 34 to terminals 26 and27. The superposition of voltages V, and V is such that, as in FIG. 4, adisplay is produced between distances x, and x, in the form of a narrowdark image. If the reference voltage V is held constant while theunknown voltage V, is varied, the narrow, dark image or window retainsits fixed width, and is moved perpendicular to its thin dimensionproportionally along the interdigital electrodes. The distance betweenx, and x, may be made quite small, so that the width of the displaywindow is quite small, resembling the needle of a conventionalelectrical meter. In any event, the location of its centroid isproportional to the unknown voltage and that voltage value may be readoff in the conventional manner using a scale engraved on the outersurface of plate 10, for example.

It is acceptable for some purposes to reverse the roles of voltages V,and V in any event, if voltage V, is held constant while voltage V, isvaried, the width of the window (or the distance between x, and x, inFIG. 3) is proportionately varied. Regular or equal incrementalresistance changes between the several sections 54 through 59 may beemployed in a linear manner (FIG. 3 or FIG. 6), or the changes may bemade non-linear by corresponding non-linear successive impedance changesof the sections so as to produce non-linear displacement of the display(FIG. 2 and FIG. 4). Altematively, as in FIG. 6, the elongatedistributor conductor 31 may contain short sections 71 and 72 at itsends that are of relatively high conductivity, with its primary and mostextensive section 70 having high impedance or resistivity. The ends 71,72 are brought out to expose terminals 27, 28 which are connected acrosspower source 35, as before. It will be understood that V and V, may beeither unidirectional or alternating voltages.

The preferred operation of the apparatus is according to a modeemploying strictly electric-field sensitive electrode configurations andnematic liquid crystal mixtures having relatively high dielectricanisotropy. Being a field-effect display, it is important for optimumperformance that the nematic liquid crystal molecules have a definiteorientation in the absence of an applied electric field. One suchorientation is the homeotropic ordering discussed with regard to thebirefringence sensitive arrangements of the R. A. Soref US. patentapplication Ser. No. 264,679 for Liquid Crystal Display Apparatus, filedJune 20, 1972 and assigned to the Sperry Rand Corporation. Other highlysuitable arrangements, include a spontaneously twisted arrangement ofmolecules that gives rise to useful rotary electro-optical effects andpermits use of very thin cells, as disclosed in the R. A. Soref patentapplication Ser. No. 363,921 for Rotary Electro-Optical Effect LiquidCrystal Display Apparatus, filed May 25, I973 and assigned to the SperryRand Corporation. The thin nematic layer in which the desiredelectrically controllable effects are to be viewed may be selected fromwell known liquid crystal materials, including mixtures of known nematicliquid crystals having storng positive dielectric anisotropy, operatingat relatively low drive voltages at room temperature, and composed, forexample, of equal molar proportions of the known nitrile Schiff bases.Preferred materials have a relatively large positive dielectricanisotropy, such as e 25 and i 8.

Since birefringence or similar electric field sensing effects areemployed in the invention, rather than the prior art turbulence effect,the invention is completed as shown in FIG. 1 by the use of an opticalcircular polarizer 45 spaced from or attached to the exterior surface ofthe plate 10. Further, a mirror 42 is attached to the exterior surfaceof plate 11, since the display is normally used in the reflective mode.The arrangement of circular polarizer and mirror in FIG. 1 pertainsspecifically to an induced birefringence kind of display in which theinitial molecular ordering is perpendicular to plates 10 and 11. If theinitial ordering were twisted, it would be necessary to use two linearpolarizers as described in the above mentioned patent application Ser.No. 363,921. Since the light rays 41 seen in FIG. 1 may approach theelectro-optical device from a variety of angles, a correspondingmultiplicity of imaging or parallax effects may be viewed by the eye at40. Since the light rays 41 pass through the region of the liquidcrystal material 12 twice, these images appear to emanate from locationswhere the rays strike mirror 42, rather than strictly from the plane ofintersection with the liquid crystal layer. Parallax is minimized bylocating the reflecting plane of mirror 42 as close as possible to theliquid crystal layer. For this purpose, the plate 11 is thinned as muchas possible consistent with maintaining proper mechanical strength and adiffusing mirror 42 is formed directly on the thinned wall. Mirror 42 isthus designed for providing diffuse reflection and consequently forpermitting wide angle viewing of the display with substantially nomultiple imaging. The effect of the electric field applied throughterminals 26, 27, and 28 is observed in the preferred form of theinvention by direct viewing with the eye, as at 40 in FIG. I, diffuseambient light as represented by rays 41 that pass through circularpolarizer 45 and through plate 10, the liquid crystal material in region12, and the plate 11, thereupon to be reflected by the diffuse mirror 42affixed to the exterior surface of plate 11. The reflected lightretraverses the region 12, plate 10, and circular polarizer 45 to reachthe eye at 40. Operation of other optical aspects of the invention isgenerally as explained in the aforementioned patent applications.

According to the invention, a flat panel, electric field controlleddevice is provided for the measurement or display of electricalparameters such as voltage, the voltage sensing effect being provided bya nematic liquid crystal medium having high positive dielectricanisotropy and placed in a thin flat-sided optically transparent cellhaving suitable electrodes. Optical transmission of the nematic liquidcrystal medium is controlled by voltages applied to interdigital arraysof parallel electrode elements affixed on the inner surface of only oneof the transparent parallel cell walls. Continuous relative changes inthe respective potentials applied to the electrode arrays providecontinuous analog movement of the borders between birefringent andnonbirefringent areas formed in the liquid crystal medium.

In a representative device, one set ofdigital electrode elements may beoperated at a selected potential from a first source, while individualsof the second set are operated at progressively varying potentialsthrough the use of a high impedance distributor conductor across which asecond potential source is connected. lf the first voltage is heldconstant while the second is varied. a dark, narrow but fixed-widthimage simulating, for example, a voltmeter needle, may be moved acrossthe display. Alternatively, a dark bar can be made to elongate acrossthe display in response to an analog voltage. Whether a moving bar orneedle is obtained depends in part upon the relative phases of the twovoltage sources.

Other display effects may be achieved. Because of the three inputterminals employed in the invention, two voltages may be applied tocontrol the movement of the display image by adjusting in time themagnitudes of either or both of the voltages. The device may be designedwith two electrode arrays both like the array associated with the highimpedance distribution conductor 31 of FIG. 2; thus. four inputterminals may be made available for applying voltage gradients acrossboth of the opposed arrays.

A particular feature of the invention lies in the fact that the highimpedance distribution system beneficially prevents imposition ofexcessive voltage gradients within the liquid crystal medium,destructive gradients which would induce dielectric breakdown and arcingthrough the liquid crystal medium. The impedance of the distributionsystem is chosen high enough to reduce power consumption for the drivesource to an acceptably low value.

While the invention has been described in its preferred embodiments, itis to be understood that the words which have been used are words ofdescription rather than of limitation and that changes within thepurview of the appended claims may be made without departure from thetrue scope and spirit of the invention in its broader aspects.

l claim: 1. Electric field sensing display apparatus comprismg:

first and second coplanar optically-transparent array means havingrespective first and second interleaved pluralities of electricallyconductive elongate electrode means for defining electric field patternstherebetween, first optically transparent plate means having firstsurface means for supporting said electrically conductive elongateelectrode means in spaced substantially parallel alternate cooperativerelation,

first elongate distributor means affixed to said inner surface means andcoupled at one end of each of said first plurality of electricallyconductive elongate electrode means at spaced intervals along said firstelongate distributor means.

second elongate distributor means affixed to said inner surface meansand coupled at one end of each of said second plurality of electricallyconductive elongate electrode means at spaced intervals along saidsecond elongate distributor means.

at least one of said first and second elongate distributor means havinga substantially high impedance characteristic with respect to said firstand second interleaved pluralities of electrically conductive elongateelectrode means,

second optically transparent plate means in substantially parallelspaced relation with said first optically transparent plate means andhaving second surface means,

wall means for completing enclosure means defined in part by said firstand second optically transparent plate means,

terminal means exterior of said enclosure means adapted to be coupled toa voltage source for producing a voltage gradient along said elongatedistributor means having a high impedance characteristic, and

electric field sensitive means disposed within said enclosure means forcontrolling the degree of optical transmission of said electric fieldsensing display apparatus in accordance with the value of said voltagegradient.

2. Apparatus as described in claim 1 wherein said first elongatedistributor means is coupled at one end of each of said first pluralityof electrically conductive electrode means at substantially equallyspaced intervals along said first elongate distributor means.

3. Apparatus as described in claim 1 wherein said high impedancecharacteristic is constant along the region coupled to said firstplurality of electrically conductive elongate electrode means.

4. Apparatus as described in claim 1 wherein said high impedancecharacteristic progressively varies along the region coupled to saidfirst plurality of electrically conductive elongate electrode means.

5. Apparatus as described in claim 1 wherein said electric fieldsensitive means comprises a liquid crystal material demonstratingpositive dielectric anisotropy.

6. Apparatus as described in claim 5 wherein the thickness of saidliquid crystal material between said first and second surface means liessubstantially between 0.5 and 2.5 microns.

7. Apparatus as described in claim 5 wherein the thickness of saidliquid crystal material between said first and second surface means liessubstantially between 1.4 and 1.9 microns.

8. Apparatus as described in claim 1 wherein at least one of said firstand second elongate distributor means has a high electrical conductivitycharacteristic substantially equal to the electrical conductivitycharacteristic of said first and second interleaved pluralities ofelectrically conductive elongate electrode means.

9. Apparatus as described in claim 1 including terminal means exteriorof said enclosure means adapted to be coupled to a second voltage sourcefor placing the entirety of said elongate distributor means having ahigh electrical conductivity at substantially the voltage of said secondvoltage source.

10. Apparatus as described in claim 5 further includmg:

optical polarizer means pennitting illumination of and viewing of saidliquid crystal electric field sensitive means therethrough, and

mirror means spaced from said liquid crystal electric field sensitivemeans opposite said optical polarizer means for returning light throughsaid apparatus.

1. Electric field sensing display apparatus comprising: first and secondcoplanar optically-transparent array means having respective first andsecond interleaved pluralities of electrically conductive elongateelectrode means for defining electric field patterns therebetween, firstoptically transparent plate means having first surface means forsupporting said electrically conductive elongate electrode means inspaced substantially parallel alternate cooperative relation, firstelongate distributor means affixed to said inner surface means andcoupled at one end of each of said first plurality of electricallyconductive elongate electrode means at spaced intervals along said firstelongate distributor means, second elongate distributor means affixed tosaid inner surface means and coupled at one end of each of said secondplurality of electrically conductive elongate electrode means at spacedintervals along said second elongate distributor means. at least one ofsaid first and second elongate distributor means having a substantiallyhigh impedance characteristic with respect to said first and secondinterleaved pluralities of electrically conductive elongate electrodemeans, second optically transparent plate means in substantiallyparallel spaced relation with said first optically transparent platemeans and having second surface means, wall means for completingenclosure means defined in part by said first and second opticallytransparent plate means, terminal means exterior of said enclosure meansadapted to be coupled to a voltage source for producing a voltagegradient along said elongate distributor means having a high impedancecharacteristic, and electric field sensitive means disposed within saidenclosure means for controlling the degree of optical transmission ofsaid electric field sensing display apparatus in accordance with thevalue of said voltage gradient.
 2. Apparatus as described in claim 1wherein said first elongate distributor means is coupled at one end ofeach of said first plurality of electrically conductive electrode meansat substantially equally spaced intervals along said first elongatedistributor means.
 3. Apparatus as described in claim 1 wherein saidhigh impedance characteristic is constant along the region coupled tosaid first plurality of electrically conductive elongate electrodemeans.
 4. Apparatus as described in claim 1 wherein said high impedancecharacteristic progressively varies along the region coupled to saidfirst plurality of electrically conductive elongate electrode means. 5.Apparatus as described in claim 1 wherein said electric field sensitivemeans comprises a liquid crystal material demonstrating positivedielectric anisotropy.
 6. Apparatus as described in claim 5 wherein thethickness of said liquid crystal material between said first and secondsurface means lies substantially between 0.5 and 2.5 microns. 7.Apparatus as described in claim 5 wherein the thickness of said liquidcrystal material between said first and second surface means liessubstantially between 1.4 and 1.9 microns.
 8. Apparatus as described inclaim 1 wherein at least one of said first and second elongatedistributor means has a high electriCal conductivity characteristicsubstantially equal to the electrical conductivity characteristic ofsaid first and second interleaved pluralities of electrically conductiveelongate electrode means.
 9. Apparatus as described in claim 1 includingterminal means exterior of said enclosure means adapted to be coupled toa second voltage source for placing the entirety of said elongatedistributor means having a high electrical conductivity at substantiallythe voltage of said second voltage source.
 10. Apparatus as described inclaim 5 further including: optical polarizer means permittingillumination of and viewing of said liquid crystal electric fieldsensitive means therethrough, and mirror means spaced from said liquidcrystal electric field sensitive means opposite said optical polarizermeans for returning light through said apparatus.